Manufacture and testing of fiber mats



4May 8, l1945. H. w. ANWAY MANUFACTURE AND TESTING oF I'BER MATs Filed Jan. 15,"194o ?atent`ed May 8, 1945 Fries 2,375,182 MANUFACTURE AND rEs'rlNG or mea Mars Herman Anway, Cloquet, Minn., assior Wood Conversion Company, Cloquet, n.' I,

l corporation of Delaware Application ljanuary l5, 1940, Serial No. 313,919

,15' Claims.

The present invention relates generally to felted fiber masses, such, for example, as are used for thermal insulation. In particular it relates'to the formation of felted masses'which have high resilience and high resistance to settling under impact.

Certain uses fof felted i'lber as insulation in house Walls, in vehicles, such as refrigerator cars, and particularly in refrigerator doors, are at# tended with the development-of settling of the fibers in a space originally packed uniformly with the felted mass. This does not always occur, but it is more likely to occur when effort is made to have a low density of mat. Certain low densities are indicated not only for economy, but also for maximum thermal eiliciency. However, where settling occurs, the insulation is destroyed and both objectives of economy (based on insulation effect obtained) and thermal efiiciency are lost.

Heretofore, there has been no guiding knowledge to correct such'faults, and such correction as has been employed to prevent settling has operated against economic use of bers and high thermal efficiency.

The present invention is the result of studying fibrous masses to ascertain the fundamental causes of settling under impact. As a result of the studies, it is now possible to determine the. settling characteristics of a particular fiber, or a mass thereof, so that a'body of felted fibers for insulation or other uses may be formed to resist settling under a speciiied maximum impact corresponding to the particular use.

Another characteristic of such masses is the elasticity of the felted mass. Heretofore, prevention of settling has been attempted by making space, then to compress the mass, and confine it while compressed into the space. This has not always been successful. it has been found that the mass not only loses elasticity, but that it `does settle. r f

Studies of ber masses have also revealed that several blocks of felted lbers, each containing! the same volume and weight of the same fibers, may

felted. A second block may be confined and exert pressure less than said value, and maintain it without loss. A third block may be unconned and be subject to a compression force up toa maximum' value with substantially 100%-` elasticity. The present invention explains these conditions and makeslpractical use of them.

A mass of fiber may be subjected to an impact or a compression force and then released, so as to be compressed and then expanded. It may be slightly compacted so that after the impact or compression, and expansion, it Pretains a portionl of the compression. This exemplifies elasticity lesstlian 100%. It has been determined that it l becomes more highly felted by such an impact or felted masses for certain spaces, larger than the p Iihe present invention shows that the elasticity or resilience of. a -felted mass, and its tendency to settle are related properties. It also showsthat as the resistance to settling is increasedthe elasticity is made more stable. in the extreme case', the invention enables one to make a, .felted 4mass Aresistant to settling under the force of a prescribed maximum impact or force of compression, and the resilience of the felted mass is a maxi` mum and' is permanent, except as the fibers per vse may change resilience by aging, wetting or other factor not related tothe mass condition ofy the ber.

com-pression. If the same impact force is repeated once again, the same kind of results occur.

f particular impact or compression force becomes satisfied and the mass is considered to be subf" stantially 100% felted. Thus, theresilience of the 100% felted mass is stable and canbe utilized.

such compression maintained, and -then released, without loss ofthe resilience. Y

results obtain, but the degree of felting is correspondingly less or greater, yet substantially 100% for that force or thatimpact employed.

Studies of a' mass of nbers, which per se have resiliency, have revealed some unusual and uny expected properties. For example, if a mass of loose bers is-compressed and quickly released each compression is halted without release, for varying periods of time, and then released, the extent of expansion 'or spring-back decreases with the time of halting. In my copending application Serial No. 313,920, filed January 15, 1940, now U. S. Patent No. 2,325,026, issued July2'7, 1943, this has been explained in connection with analytical procedures for examining fibers. explanation for the purposes of the present invention, it is stated that4 any compression o! a mass of bers beyond its latent elastic limit tends to felt the bers more and more. However, this is a slow process, and so slow, that any ordinary movement of compression proceeds faster than the felting action. Thus, on halting such compression as above stated the elasticity of the mass tending to expand it, is exerted on the mass while the felting process continues, Thus, the force tending to expand the mass of bers referred to is gradually dissipated by producing felting.

It follows that a given volume of felted bers may have an unsaturated. capacity for being felted. This capacity operates against having' a high degree of elasticity in the mass which will .persist during compression. In other words such a mass exhibits a false total resiliency, which is not stable or lasting, and which hides the true elasticity. Therefore, there are numerous objects of the invention.

One object of the invention is to test bers to determine their tendency to settle, and to determine the conditions which must be imposed to make a ber mass resistant to settling against an applied force of compression, or impact, of a specified maximum value, or the conditions of a certain usage.

It is an object of the present invention to provide more stability in the resiliency o f a felted mass oflbers.

It is another object of the invention to provide a maximum of. stable resiliency in a mass of fibers, within certain limitations of applied force.

It is `also an object of the invention to provide a mass of fibers with its capacity for felting, under certain conditions, substantially saturated,

Awhereby the resiliency is enhanced and stabilized.

Various other and ancillary objects and advantages of the invention will become apparent from the following description and explanation of the invention.

The invention may best be understood from the following explanations of behaviors, 4which are hereinbelow -described with reference to the companying drawing, in which:

Fig. 1 is a plot representing the gradual dissipation of pressurev from a conned compressed mass of bers.

Fig. 2 is a diagrammatic representation of a mass of fibers subjected to repeated applications and removals of the same compressive force.

-Fig. 3 is a graph showing the change of volume of three like masses of ber each subjected to a different impact to cause settling.

Fig. 4 represents a cylinder calibrated to indicate the settling of fibers therein, such as is used' to obtain the graphs of Fig. 3.

Fig.5 is a graph showing the drops in compressive force and spring-back in repeated compressions of the same mass to the same ultimate volume.

A mass of 158 grams of ber derived from' wood is placed in a cylinder'of 8 inches diameter and compressed to a volume of 3.15 board feet (one board foot equals 12 x 12 x 1 inches) per pound of ber, by pressing down a plateover the ber.

The containeris set on a scale platform which registers the pressure. The pressure is immediately recorded, and again at later time intervals. It gradually drops, as represented ln Fig. 1 wherein axis I0 represents time, and axis 'il represents the .force as scale readings. Curve i2 represents the loss of pressure, showing it to-be rapid at rst, and slower and slower as time goes on. This clearly shows that the original resiliency is not permanent. From other studies made by the applicant', it is known that the-fiber is becoming more felted as time goes on According to the characteristics of kthe fiber, the time required to reach' equilibrium will be very great, in the order of days, during which the elastic force is gradually expended in causing internal shiftingof the fibers to increase its felted character. During this period the nberhas capacity to be felted, and in the end Will be substantiaily 100% felted and 100% elastic against a maximum force corresponding to the residual pressure.

Obviously the above procedure is not a practical one, nor a definite one for use to meet a prescribed condition. To make it useful in lling insulation spaces, it is necesary to relate the original density-to the felting and elastic properties of the fiber.

Another operation illustrates the relation of felting and elasticity. In Fig.`2 there is represented a container such as an open-top cylinder I5 filled with a mass of ber l5. A pressing plate l1 is represented to exert a definite pressure of P pounds represented. by arrow I8. These elements are repeated in the gure without the numerals. except that the ber levels are given new designations for the purpose of identification of changed conditions. The operations of the series are designated by the stations A, B, etc., to N, the latter representing the last and not necessarily the 13th compression.

The original loose mass i6 at A is compressed i by force P to the Bi level and the plate Il is then immediately withdrawn. The mass springs back to level B2. This is repeated again at station C by the same pressure Pto reach the level Ci, and the spring-back is to level C2. This is repeated numerous times as represented at vstation N byl the conditionsindicated at N1 and N2. Actually,

which capacity becomes saturated at N. The

larger spring-back at B for example is due to the unsaturated capacity for felting. As shown in Fig. 1 this observed elasticity in B is but .tem- Dorary in part, and is convertible to felting. At

N, the said temporary elasticity has been conv verted to felting, and the elasticity from N1 to Ns vis a stable or a elasticity. The block N2 when subjected to a force of P or less is substantially 100% elastic, and fully felted.

The practical application ofthis is the use of the fiber mat N of volume N1 in a confined space to resist any motion yunder a force of P or less. If block Na is used in a conned space it will temporarily compress to less volume under an impact or force of P or less, but it will expand again. Thus, where a refrigerator door, for example. is

insulated with a mass of the fiber, and the door asraia is subjected to impact havin not a force component greater than force Rte ilber should be used at the density of block Nr to be immovable in the door. v

This explanation raises the question as to what happens at forces greater than P. The answer is obvious and has been proven by experiments. If the mass of liber N2 is considered in a new series as A of Fig. 2, wherein the new P is a greater force, the same results are observed.

Fig. 3 is a graph showing the results 'of a sei ries of impact tests where the force varies. A

container-in the form of a sheet metal cylinder (Fig. 4) of 4 inches inside diameter has an observation slit 2! therein about 116 inch wide. The slit is calibrated in units reading board feet per pound to give directly that value. 150 grams 1;/3 of a pound) of ber are used in the cylinder. Such amount of liber to be tested is placed in the cylinderin a loose low-felted condition. The filled cylinder with one specimen is dropped 6 inches, and the resulting volume read through the slit 2 i. The impact on the looseber is thus 1/6 foot-pound. It is dropped again and again, and the volume read, until the change is practically nil. This is repeated with other like specimens of the same lliber using a drop of 1 foot to and 3 feet to give 1 foot-pound. The results are shown in Fig. 3.

In Fig. 3, the axis 23 represents the number of drops, and axis 24 the board feet per pound read after each drop. Curves 25, 26, 2 and 28 show the results respectively for the 6-inch, l-foot, 2- ioot and 3-foot drops. 'Ihe full-line portion of each curve representsthe process to its substantial end, andv observed'readings are shown. The

j dotted-line extensions show the ilnal constant location, `for which the observed readings are omitted. `They vary but slightly above and below the line. They show deiinitely that as the impact is increased, the nal settled footage deE creased.v In `the early drops the liber is not completely felted under the force applied thereto `by the impact. However, complete felting is accomplished by repetition, .which gradually increases the force effective on thebers.

A practical application of such a procedure is to test a viiber to see what volume` a given fiber will have when completely felted to resist settling by any selected -maximum impact. Thus, reading from Fig. 3, it is learned that if a refrigerator door is not subjected, as in closing, to an im-v jected to such impact, the particular fiber testedv must be compressed to a footage of not more than approximately 3.75 board feet per pound, and of course preferably slightly less than that limit for a margin of safety. Where the liber so used is conned, mere compression is sumcient. Where it is not confined, it must be treated so as to completely felt it at that footage for the specied impact.

Figs. 2 and 3 represent ultimately the same thing. The condition of block N2 is the expanded form, which is also read in cylinder 20 and plotted in Fig. 3. In applying the knowledge derived from Fig. 2, it is obvious that where the critical footage of Fig. 3 is employed as determined, it is preferable to pack it in an insulating space, in its compressed footage as indicated by block N1. Therefore, in preferred practica-the footage at which the belrs should be conned in a refrigerator door is less than the critical footage so that it is resiliently held in its chamber. Any

dit

compression or impact by suitable force until the resistance to itis stabilized. However, the use of the same force or the same' impact for repeated applications is not a limitation. Initially, in Fig. 2, the applied force may exceed the maximum ultimatevalueso long asthe feltingintroduced by such excessive force does not exceed the felting to be attained at s'tation N in Fig. .2. Likewise, in Fig. 3, the initial drops o f the cylinder may be at a greater height than shown, so long as the feltn'g thereby introduced-is not in excess oi the felting desired for the specified felting impact. Use of greater forces in the initial stages aids merely to shorten or hasten the procedure. However,. this is not required nor is it desired, because it robs the process of its ease of control and .introduces the problem of taperingoil' the excess of force.

`The invention' broadly contemplates -that initially such excessive force may be used. However, practically, the preferred procedure for testing iiber, and for preparing iiber masses for speciiicatins, is to .use repeated compression forces or impacts of the same value.

Broadly, the application of compressive force or oi impact to the liber-mass, is the doing of mechanical work on the mass. Mathematically, work is the product of multiplying force by the distance through which it ac ts. I Impact is work;

In the procedure'o Fig. 2, the force illustrated is'constant, and as the shrinkage of the mass under that vforeegrows less -and less, the product of the force and the shrinkage at each application, namely, the work, grows less and less.'

In the case of Fig. 3, 'the impact or work illustrated is constant. But asv the shrinkage or settling is less and less at each impact, it follows that the resulting force eective on the fiber must increase, in order that theiworis be constant. In the impact process, the procedure does not determine or evidence the actual value of the force effective on the iiber, nor the compression of the 1 column resuiting from such force. The compression takes piace nt the moment of impact, and

then the spring-back occurs. Obviously the force ed'ective on the fibers increases to a substantially constant value when the settling has substantially approached its limit. This final force mayv be determined approximately by measuring the maximum permanent spring-back of the co1- umn, or theforce necessary to be applied to obtain repeatedly the maximum spring-back.

Therefore, in the appended claims the terms referring to Work contemplate both described methods, as well as other methods. The work is expended in overcoming friction of the ber mass sliding in its container, inovercoming the instant Part of the lease and withdraw the plate to permit immediate spring-back (as described in my copending application Serial No. 313,920, filed January 15,

V194:0, 110W U. S. Patent Nb. 2,325,026, issued July 2'?, 1943). In the present example, the ber mass is compressed to 3.15 board-feet per pound in each instance of compression. At this footage the compressing force is read, and the bers allowed to spring-back to a higher footagawhich is also read. This process is repeated until the compressive force and the spring-back footage are substantially constant. As shown in the plot, less than 12 compressions accomplish this.

In Fig. 5 the results are shown on a graph, in which the axis 30 represents the number of 'the compressions. Axis 3| represents the total compression force in pounds to obtain a footage of 3.15 board-feet per pound. Axis 32 represents the board-feet per pound attained on spring-back. Horizontal line 33 represents the compressed footage of 3.15 board-feet per pound. Line 34 repre- Y sents the smooth curve on observed points of recorded force at 3-.15 footage. Line 35 represents I the smooth curve of observed points of springback height. The level of line 35 above line 33 represents the spring-back. It is seen that it decreases until it is substantially constant. This shows that a mat has been formed with substantially 100% elasticity and 100% felting for a compression force of 47 pounds at an expanded footage of 4.2 or elastically compressed footage 3.15. The higher initial resiliency evidenced in the earlier compressions reects the true elasticity and also the capacity of the initial mats to be felted. f

Considering the results of Fig. 5 in the terms of work, it is seen that in the end, the final force has become constant, and the distance through l which it moves has become constant. Thus a constant amount of work is done on the mass at each compression, and the work is substantially all recovered in the spring-back'. Neither the force nor the work is constant in the early part of the process. Originally, with a highest force accompanied by greatest spring-back, there is the greatest input of work. A large fraction of this goes into felting. As the capacity for being felted becomes saturated, less work is performed. The process automatically limits the work, so that in the end, it is just enough to satisfy the 100% resiliency of the resulting mat. The mat is 100% felted with respect to the force which is attained when the 100% resiliency is satisfied on compress ing the nal mat from footage 4.2 to 3.15.`

The product As the foregoing description indicates, any felted mass of bers has substantially 100% resiliency to some unknown but determinable force or impact. At such condition, it has also substantially 100% saturation of its capacity to be felted under the said force or impact. Given standard is commercially impossible to have standard,

bers. Fibers of any given kind vary from time to time and from batch to batch. Measures of i these variations are the properties for felting, the

elasticity, and the/free footage (the density at zero compression). ESuch properties are described with methods of determination in my copendlng application Serial No. 313,920, led January l5, 1940. These are affected by variations in the material-of the ber, the particle sizev distribution, and any special treatments, sizing or impregnation of the bers. Two batches of bers may vary considerably in these properties, which determine the critical densities for critical effects herein described.

Accordingly, the use of a suitable density of one batch of ber for meeting the critical specications, is no precedent for choice of that density for another batch of like i'lbers. For any batch of bersthe specication is prior, and by this invention the -density to meet the specifications critically is not prior, but subsequent to the specications. Given the specifications, and the ber, the critical density may be determined as herein described.

The present invention therefore reduces uncertainty, guess-work, and waste by over-caution, to a practical certainty, precise measurement, and elimination of waste. For insulation purposes it permits using minimum densities tovmeet physical requirements, and thereby permits obtaining the best thermal emciency consistent with such requirements. Heretofore, where very high den-l sities have been used blindly to meet the physical requirements, thermal insulation eiiiciency has The. present invention is applicable to many kinds of bers such as mineral Wools, red Wood bark, forms of cotton, jute, hair, Kapck,exce1sior, and other materials capable ofbeing felted.

In practicev it has been successfully demonstrated in use of wood ber produced by the process ofAsplund U. S. Patent No, 2,008,892, wherein the damp product taken directly from the machine is rdried to an linsulatirug fiber. In such process the setting of grinding disks may be very slightly varied mechanically, orby wear, to

'change the particle size distribution of the ber.

bers and empirical knowledge of densities and ciency for otherwise meeting demanding physical requirementsto maintain that efficiency.

Impact `resistance Accordingto the principles herein disclosed, numerous tests may be established as standard to indicate a property of the ber. The term impact resistance has been adopted as such a property for purposes'oiy evaluation of bers, and

it is defined es the board-feet per pound nally attained by a column of ber when repeatedly subjected' to an impact of 1 foot-pound, -by dropping the column. i

There is considerable experimental error of observation and some variance in reading the so-called substantially constant values at consecutive readings at lnal conditions. The results are however remarkably accurate and consistent considering the character of apparatus and the heterogeneous character of a ber mass. Accordingly,in following the present invention it is I 2,875,182 contemplated that the term "substantially con-- stant or substantially 100%" not only express the ideal but also the practical limit, and the claims should be construed accordingly. If a large volume of fiber is at hand there may be error in sampling to be added to the possible errors in testing the specimen. For greater accuracy, several specimens may be tested and the results averaged. `Setting materials to limits -usually calls for excess caution to give a margin .In order to illustrate hovg this may be applied,`

of safety. v

Therefore, in meeting a specification wherein a margin of safety is commonly entered, it is practically suicient to attain 90% of the ideal.

I claim: I

I, 1. The method of testing fibers to -determine the minimum non-settling density thereof` with respect to a pre-determined maximum impact,

the disclosed three procedures are discussed lwith reference to this 90%.

-In the repeated application` of constant pressure, as inv Fig. 2, it is suiiicient that either the vfinal volumes N1 or N2 in consecutive compressidered in the circumstances to be substantially constant or substantially 100% completed.

In the impact procedure as in Fig. 3, the ilnal volume readings at consecutive dropsvof the curve formed, may agree withinv 10% of each other, one way or the other, and be considered substantially constant or substantially .100% completedn Thus for example in curve 28, the last two plotted readings are actually 3.8 and 3.75, which agree Within 1.5%. On another specimen an attempt to duplicate curve 28 might give final readings checking within the curve as close as that 2.5% but falling above or below the level of curve 28 with a variance as much as 10%.

In the constant volume compressionoi Fig. 5, it is seen by the plot that actually the values for curve 30 at the 5th and A6th drops show deviation from the smooth curve. The readings were 58 and 50 pounds. This is a deviation of 13.8% or 16% depending on the base taken, and it is indicated by the curve that the process has not reached an equilibrium condition. Reproducing curves Iii and with another specimen might give results diiering from those shown, but an agreement within 10% is considered acceptable and within the scope of the present invention.

In the processes above described the repetitive which comprises subjecting a mass of said fibers to repeated impacts of said predetermined maximum until no further 'change in the'free volume of the mass is-eifected by the repetition, and v measuring the resultinglettled density.

2.' The method of testing fibers to determine the minimum density thereof to resist movement under an impact of predetermined maximum value, which comprises subjecting a mass of said fibers to repeated impacts of said predetermined maximum until no further change in the free volumeof the mass is effected by the repetition, and measuring the density of the resulting settled mass when compressed to its elastic limit.

3. The method of testing fibers to determine the minimum non-settling density thereof with respect to a predetermined maximum compression force, which comprises subjecting a specimen of the bersto repeated compressions by said predetermined-maximumfforce until a substantially constant volume isattained on removal of the compression at repeated applications, and determining the density of the resulting mass.

4: The Amethod of making an ultimate resilientv felted mass 'of dry ber which mass has an uncompressed fixed densithwhich mass is responsive resiliently u,to compression forces up to a predetermined magnitude of pressure, and which mass is responsive to a pressure of greater magnitude by being additionally felted to an uncompressed densitygreater than said fixed density,

which method comprises as a rst operation do-' ing mechanical work-on an initial mass of dry bers which initial mass has an uncompressed density less .than said fixed density, said work effecting a compression beyond the elastic limit of said initial mass whereby the felting of the steps alter the characteristics of the f ber mass lby addition, with increments of density, ofifelting,

' Zero.

It is therefore believed that after reading and understanding tie invention, and appreciating the factors which may alter results, one may follow the teachings hereof, and achieve the desired results with an accuracy from 90% to 100%,

however the basis for such percentage is taken.

From the foregoing it will be appreciated that the invention has several aspects, and that various modifications may be practiced, without-departing from the invention as expressed in the appended claims.

mass is increased toward but not in excess of the degree of feltingH of v'the ultimate mass to be formed, expanding the compressed mass to exert available elasticity therein whereby to4 form a resulting mass having an uncompressed density greater than that of said initial mass and less than that of said ultimate mass, and repeating the said compression and expansion a plurality of times on the successive resulting masses, wlfereby in the repetition the resulting masses of the fiber become additionally felted and have greater uncompressed density by increments of both felting and uncompressed density which increments decrease and approach Zero, and ceasing said repetition when said increments are substantially zero, whereby the resulting mass'is said"I ultimate mass.

y5. The method of making an u1timate resilient- Iof the same value and such that said ultimate mass is stable against further felting and further increase in uncompressed density under such impact, whereby as the impacts are repeated the resulting masses of the ber become additionally` .felted and have greater uncompressed density by increments of both felting and uncompressed density which increments decrease and approach zero, and ceasing said repetition when said increments are substantially zero, whereby said ultimate mass is formed.

6. The method of maldng an ultimate resilient felted mass oi dry fiber which mass has an uncompressed xed density, which mass is responsive resiliently to compression forces up to a predetermined magnitude of pressure, and which mass is responsive to a pressure of greater magnitude by being additionally flted to an uncompressed density greater than said fixed density, which method comprises subjecting to repeated applications of and releases .from a compressing pressure of thesame magnitude an iniital mass of dry bers having an uncompressed density less than said fixed density, the magnitude of said pressure being such that said ultimate mass is stable against further feltingand further increase in uncompressed density under the action of said pressure, whereby as the compressions and releases are repeated the resulting masses of said fiber become additionally felted and have greater uncompressed density by increments of both felting and uncompressed density which Iincrements decrease and approach zero, and ceasing said repetition when said increments are substantially zero, whereby said ultimate mass is formed.

1. The method of making an ultimate resilient felted mass of dry iiber which mass has an uncompressed xed density, which mass is responsive resiliently to compression forces up to a predetermined magnitude of pressure, and which mass is responsive to a pressure f greater magnitude by being additionally felted to an uncompressed density greater than said tlxed density, which method comprises subjecting to repeated compressions to the samel ultimate volume and repeated releases an initial mass of dry bers having an uncompressed density less than said fixed density, the said volume being that at which the said ultimate mass is compressed to itsl elastic limit and to a density beyond which further compression produces additional felting and an uncompressed density greater than said iixed density,

density, whereby upon each release the said compressed volume expands to a corresponding uncompressed volume, said compressions being each beyond the elastic limit of each mass compressed whereby felting in the resulting masses is increased by increments which approach zero, and whereby the forces exerted in attaining said volume gradually decrease by decrements which approach zero, and whereby the said uncompressed volumes after the releases decrease by decrements which approach zero, and ceasing said repetition when said decrements are substantially zero.

9. A mat of dry fibers resulting from the process of claim 4.

10. A mat of dry bers resulting from the process of claim 5.

11. A mat of dry fibers resulting from the process of claim 6.

l2. A mat of dry fibers resulting from the process of claim 7.

13. A mat of dry bers resulting from the process of claim 8. i y, l

14. The method of producing thermal insulation of felted dry bers in a body having a space to receive insulating fibers, while preventing danger of settling of the bers in said space by impacts in magnitude less than and equal to an impact of a predetermined maximum value,

l which comprises providing a uniform supply of whereby as said compressions and releases are feltable ultimate mass of dry fibers characterized by resiliency in slight compression and by a iixed uncompressed density, which comprises subjecting to repeated compressions to the same ultimate compressed volume and repeated releases therefrom an initial mass of dry fibers having any uncompressed density less than said fixed bers in bulk form which fibers felt on packing, said bulk form being such that the bulk requires packing and densifying to provide said mass, subjecting a representative specimen of ber selected from said uniform supply to the process of claim 5, wherein the value of the impacts is the said predetermined maximum value,. determining the uncompressed density of the resulting ultimate mass of bers, and packing a representative mass of bers derived from said supply into said space at a density equal to said determined density, whereby said packed fiber is permanently non-settling under impacts of value not in excess or said predetermined maximum value.

15. The method of producing thermal insulation of felted dry fibers in a body having a space to receive insulating fibers. while preventing dany ger of densication of the mass of iibers in said space under the inuence of compressing forces in magnitude less than and equal to a force of a predetermined maximum value in pressure, which comprises providing a uniform supply of fibers in bulk form which bers felt on packing, said bulk form being such that the bulk requires packing and densifying to provide said means, subjecting a representative specimen of fibers selected from said uniform supply to the process of claim 6 wherein the pressure employed is said predetermined maximum pressure, determining the uncompressed'density of the resulting ultimate mass of fibers, `and packing a representative mass of `iibers selected from said supply into said space at a density equal to said determined density.

. HERMAN W. ANWAY. 

